geog 370 theory!

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177 Terms

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geographic information

data that can be given a location in space (latitude, longitude)

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earliest GIS use

John Snow's 1854 Cholera outbreak map

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geographic information system

a system to organize, analyze, and visualize spatial data

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discrete raster

classification of features in a landscape

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continuous raster

resulting from measurement of an environmental variable such as temperature, elevation, etc.

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data resolution

city, county, state, etc

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global positioning system

efficient way to find a point in space and navigate to that point

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trilateration

process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres, or triangles

intersection of the satellite ranges, at least 4 needed

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factors to improve GPS measurements

- receivers have a book to know when/where to expect a satellite

- satellites are in predictable orbits

- correction signals are sent from the satellite

- SBAS (WASS and EGNOS)

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causes of measurement errors

changes in satellite orbit, the clock isn't perfect, selective availability

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selective availability

got or military decision to add error on purpose

limit access

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multipath effect

interference of buildings, trees, or mountains that result in the receiver not getting / reflecting signals

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differential GPS

a correction method that uses a series of base stations at known locations on the ground to provide a correction of GPS positional information

can be processed in real time (requires a radio or cellphone signal) or later on

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coordinate precision

each degree (111 km): location of a small country

1st decimal (11.1 km): positions of large cities

2nd decimal (1.1 km): positions of villages

3rd decimal (110 m): ID a large field/campus

4th decimal (11 m): ID a parcel of land, typical uncorrected GPS unit

5th decimal (1.1 m): distinguish trees from each other

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categorical rasters

the number attached to each means a category

can be very useful for chloropleths

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ellipsoid

a model of the rounded shape of earth

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semi-major axis

half of the longest diameter of an ellipse

goes from east to west

<p>half of the longest diameter of an ellipse</p><p>goes from east to west</p>
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semi-minor axis

half of the short axis of an ellipse

goes from north to south

<p>half of the short axis of an ellipse</p><p>goes from north to south</p>
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datum

defined by ellipsoid and set of points to anchor the Earth's surface to the model ellipsoid

defines the radius, inverse flattening, semi-major and semi-minor axes for an ellipsoid

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flattening/inverse flattening

represents the top and bottom squishing of the Earth when projections are completed

(major - minor) / major

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projection

making something spherical flat

will distort shape, area, direction, or distance

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great circle distance

shortest distance between 2 points over the surface of a sphere

why plane flight paths look curved

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conformal projections

preserve shape

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equivalent/equal-area projections

preserve area

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equidistant projections

preserve distance

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azimuthal projections

preserve direction

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azimuths

lines of true direction

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standard points and lines

points or lines of intersection between the developable surface and spheroid

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tissot's indicatrix

visualizes distortion in projected map, s = "area scale" = product of semi-axes of circle/ellipse on the projected surface

<p>visualizes distortion in projected map, s = "area scale" = product of semi-axes of circle/ellipse on the projected surface</p>
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cartesian system

the system of x and y axes

attempting to keep it positive if at all possible

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geoid

mean sea level that is used to measure precise surface elevations

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coordinate system

system that uses numbers to uniquely determine a position

use cartesian, decimal degrees, or degrees/minutes/seconds

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DMS to decimal degrees

add the degree + minutes/60 + seconds/3600

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decimal degrees to DMS

name of the game is truncation

degree + remainder

remainder(60) to get the minutes, then remove the remainder there

final remainder times 60 again = add them all up together

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latitude

parallel

runs East to West, -90 to 90 degrees

<p>parallel</p><p>runs East to West, -90 to 90 degrees</p>
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longitude

meridian

runs North to South, -180 to 180 degrees

<p>meridian</p><p>runs North to South, -180 to 180 degrees</p>
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UTM

the Universal Transverse Mercator

cylindrical secant transverse mercator

60 zones, each 6° in length

the central meridian is assigned a value of 500,000 meters and equator has 10,000,000 (in each zone and overall)

KEEP IT POSITIVE

<p>the Universal Transverse Mercator</p><p>cylindrical secant transverse mercator</p><p>60 zones, each 6° in length</p><p>the central meridian is assigned a value of 500,000 meters and equator has 10,000,000 (in each zone and overall)</p><p>KEEP IT POSITIVE</p>
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state plane coordinate system

uses state/county boundaries - changes depending on the region

uses transverse mercator in the long zones, lambert conformal conic in the wide zones, and oblique mercator in the panhandle of Alaska

uses SPCS 27 (US survey feet) and 83 (the main datum and is commonly measured in meters)

<p>uses state/county boundaries - changes depending on the region</p><p>uses transverse mercator in the long zones, lambert conformal conic in the wide zones, and oblique mercator in the panhandle of Alaska</p><p>uses SPCS 27 (US survey feet) and 83 (the main datum and is commonly measured in meters)</p>
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transverse mercator

cylinder is rotated 90° (East-West) and then the reg cylindrical projection is used

<p>cylinder is rotated 90° (East-West) and then the reg cylindrical projection is used</p>
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oblique mercator

tangent line at random line (all other orientations)

projection for the panhandle of Alaska because it lays at an angle

<p>tangent line at random line (all other orientations)</p><p>projection for the panhandle of Alaska because it lays at an angle</p>
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lambert conformal conic

cone intersecting the ellipsoid along 2 standard parallels (most distortion from North to South)

<p>cone intersecting the ellipsoid along 2 standard parallels (most distortion from North to South)</p>
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mercator

3857 (based on WGS 84) - represents the world as flat

in this one, greenland is the size of Africa (distorts size)

good for a small area that keeps the shape of the features, not good at scale

coordinates are in meters (HUGE numbers)

<p>3857 (based on WGS 84) - represents the world as flat</p><p>in this one, greenland is the size of Africa (distorts size)</p><p>good for a small area that keeps the shape of the features, not good at scale</p><p>coordinates are in meters (HUGE numbers)</p>
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WGS 84

4326 - uses decimal degrees and data from a GPS

degrees between -180 and 180, lat/long

world as a rectangle (flat at the top)

best used for large scale / shape representation

not actually a projection

<p>4326 - uses decimal degrees and data from a GPS</p><p>degrees between -180 and 180, lat/long</p><p>world as a rectangle (flat at the top)</p><p>best used for large scale / shape representation</p><p>not actually a projection</p>
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georectification

method used to assign a system of coordinates related to real world positions to an entire image

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georeference

to take an image in a known coordinate system and provide the information necessary for software to understand that system

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ground control points

physical points with a horizontal coordinate system and/or vertical datum

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time-lapse images

valuable for natural resource and climate change research, urbanism and regional planning, local community engagement

<p>valuable for natural resource and climate change research, urbanism and regional planning, local community engagement</p>
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SQL

structured query language used for managing databases

comp 110 part 2

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attribute tables

columns = fields

rows = features

features can have text, #'s, date/time (if something has a leading zero, it's a string)

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NC projection

2264 (for our area); STATEFP = 37

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metadata

data that describes other data; iso2/iso3 are standardized country codes

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topology

relationship between different features on a map, allows for spatial analysis

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contiguity

polygons that share a boundary are adjacent

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common file formats

vector: .shp, .geojson, .kml

raster: .tiff, .png, .img

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height modernization

upgrading the heights given - recalibration

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reference ellipsoid

mathematical model of the shape of the Earth with major axis along equatorial radius

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conic projections

place a cone on the Earth and unwrap it

<p>place a cone on the Earth and unwrap it</p>
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cylindrical projections

place a cylinder around a globe and unravel it

mercator is the best example

<p>place a cylinder around a globe and unravel it</p><p>mercator is the best example</p>
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azimuthal projection

place a flat plane on top and watch how the light radiates

<p>place a flat plane on top and watch how the light radiates</p>
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graticule

outlines of the continents and lines of lat/long

<p>outlines of the continents and lines of lat/long</p>
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constant true direction

a straight line between 2 points will give the same direction as a compass would in real life

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winkel-tripel

a projection that compromises discrepancy in distance, area, direction

<p>a projection that compromises discrepancy in distance, area, direction</p>
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hotine oblique mercator

lies at an angle diagonally (the cylinder)

<p>lies at an angle diagonally (the cylinder)</p>
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gall-peters

size is preserved, country shape is funny

<p>size is preserved, country shape is funny</p>
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affline transformation

preserves straight lines in 2D space by scaling, rotating, translating and skewing the image

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rubbersheeting

more flexibility by bending/warping images with a 3rd order polynomial

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RMSE

root mean square error

lower means a better georeferenced image

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proportional symbol map

map that uses the size of symbols to represent a variable

<p>map that uses the size of symbols to represent a variable</p>
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query

selecting features via characteristics within their attributes

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normalize data

a process to make the data values relative to the main data values, aka make them mean something

attribute/total = percentage

attribute/universe = percentage of universe with those attributes

attribute/attribute = relational percentage

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universe

value or population that forms the base from which the data item in question is a subset

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chloropleth map

thematic maps shaded with graduated colors to represent some statistical variable of interest

<p>thematic maps shaded with graduated colors to represent some statistical variable of interest</p>
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equal interval

range into equally sized classes

best used for continuous datasets

some datasets might only have data for a small number of categories

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quantile

equal # of observations in each class, best for data that is evenly distributed

easily shows relative positions, but doesn't represent well the variety of values in each bin

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natural breaks/jenks

uses an algorithm to group values into distinct break points

best used for uneven but not skewed data

bins can be widely different in size, hard to compare maps because breakpoints are so dataset specific

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pretty breaks

separating the data where it breaks nicely and assigning the colors from there

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modifiable areal unit problem

statistical biasing when samples in a given area are used to represent information

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boolean operators

AND, OR, and NOT used in search strings to refine the scope of the search

also XOR (exclusive or)

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GPS systems by country

US: Navstar GPS (31 satellites)

Russia: GLONASS (22 satellites)

Chinese: BeiDou-2 (35 satellites)

European: Galileo (21 satellites)

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sphere

most simple model for the earth with one parameter (radius)

<p>most simple model for the earth with one parameter (radius)</p>
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horizontal datum

unique geographic coordinate system created by examining a model ellipsoid and its related parameters

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vertical datum

a baseline used as a starting point in measuring elevation values (which are either above or below this value)

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nearest neighbor sampling

this method simply selects the value of the existing pixel that is closest to the desired location

84
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binomial sampling

each cell has a random probability of being assigned 'success' or 'failure' to be included in the raster image

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sequential color scheme

the gradient of saturation or luminance of a hue represents the outcomes of an ordered variable

lightest hue is the lowest value, darkest hue is the highest

<p>the gradient of saturation or luminance of a hue represents the outcomes of an ordered variable</p><p>lightest hue is the lowest value, darkest hue is the highest</p>
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diverging color scheme

highlights an important midrange or critical value of ordered data

<p>highlights an important midrange or critical value of ordered data</p>
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qualitative color scheme

presents categorical data; different hues visually separate each of the classes

<p>presents categorical data; different hues visually separate each of the classes</p>
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intersection

the point where two layers overlap/meet

output layer has characteristics of the overlay and attributes from both input and overlay

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clip

same method as intersection visually

all attributes from the kept piece of the input layer are conserved

* clip layer attributes are not conserved

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difference

creates a new layer based on where the input and overlay layers do not overlap

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symmetrical difference

a type of GIS overlay that retains all features from both layers except for the features that they have in common

<p>a type of GIS overlay that retains all features from both layers except for the features that they have in common</p>
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union

uses the OR boolean operator

can only be used with 2 polygons

preserves all features from both

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suitability analysis

evaluating a landscape to find which areas best serve a given purpose based on a set of factors

can use as many variables as you want!

best done in GEE (is most helpful for visualizing raster analysis)

<p>evaluating a landscape to find which areas best serve a given purpose based on a set of factors</p><p>can use as many variables as you want!</p><p>best done in GEE (is most helpful for visualizing raster analysis)</p>
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aspect

the direction the slope is facing, can dictate the light display

need a digital elevation model and then the aspect tool

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aspect map applications

microclimate analysis and identification

specialized agriculture

ski slope selection

remnants of rainforest

building constraints

vegetation erosion

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zonal area statistics

statistics calculated based on the cell values of a raster

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NDVI

normalized difference vegetation index

NIR = near infrared

<p>normalized difference vegetation index</p><p>NIR = near infrared</p>
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principal point

the central point of the photo

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relief displacement

effect in a photo that results in objects looking as if they were tilted outwards from the principal point

error in aerical photography

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fiducial marks

marks at the edge of photographs which are used for locating the principal point in the image